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ProSeal - Tips needed

RidiculousM

Well Known Member
I would like to ProSeal a bulkhead in place prior to riveting, its one for the aft upper deck. Would like to do this for a few reasons, 1 - there are a few minor gaps in a few of the flanges and 2 - trying to reduce the Pucker factor on the outer skin when riveted in place. So if anyone has any tips/advice or point me to some literature on this would be great! Thanks in Advance


Mike
 
Tank sealant if not a good material choice for this.

Once cured it is a somewhat flexible rubbery substance.
not something you want filling a gap on a structural joint.
Using it between two tightly mating surfaces is fine.... just don't use it to fill gaps.
 
I'm actually working on top aft skin too. I back riveted mine. When you lay inside with a back rivet set, you can push on the back riveter with your free hand and close the gap prior to riveting. It works pretty good, better than if I didnt back rivet.
 
There's one solution given in the RV-3B plans, to remake the flanges. I had to do that a few places for my fuselage. I described it in my VAF blog in

Post #323

and

Post #330.

It seems like this will take gobs of time but it goes surprisingly fast.

Also, if you're going to use glue for holding things in place, I've been using West Systems thickened G/flex, part number K655 (I think) and it works fine. 3M's 2216 is also a good epoxy. In both cases, the joint needs proper skin prep. We don't use the epoxy for filling the entire gap directly but do use it for holding shims in place.

Some people also bond the skins to the airframe as well as riveting them. Let the epoxy cure completely before riveting if you're going to do that, of course. That technique is somewhat complicated and certainly time-consuming but can give good results. It can also make some poor work permanent, just so that you know. If you do this, first bond in the shims and then, after that's cured, bond the skin on. There aren't any real shortcuts. Like I suggested, it's a real time-suction.

Dave
 
I would like to ProSeal a bulkhead in place prior to riveting, its one for the aft upper deck. Would like to do this for a few reasons, 1 - there are a few minor gaps in a few of the flanges and 2 - trying to reduce the Pucker factor on the outer skin when riveted in place. So if anyone has any tips/advice or point me to some literature on this would be great! Thanks in Advance


Mike

Tank sealant if not a good material choice for this.

Once cured it is a somewhat flexible rubbery substance.
not something you want filling a gap on a structural joint.
Using it between two tightly mating surfaces is fine.... just don't use it to fill gaps.

There's one solution given in the RV-3B plans, to remake the flanges. I had to do that a few places for my fuselage. I described it in my VAF blog in

Post #323

and

Post #330.

It seems like this will take gobs of time but it goes surprisingly fast.

Also, if you're going to use glue for holding things in place, I've been using West Systems thickened G/flex, part number K655 (I think) and it works fine. 3M's 2216 is also a good epoxy. In both cases, the joint needs proper skin prep. We don't use the epoxy for filling the entire gap directly but do use it for holding shims in place.

Some people also bond the skins to the airframe as well as riveting them. Let the epoxy cure completely before riveting if you're going to do that, of course. That technique is somewhat complicated and certainly time-consuming but can give good results. It can also make some poor work permanent, just so that you know. If you do this, first bond in the shims and then, after that's cured, bond the skin on. There aren't any real shortcuts. Like I suggested, it's a real time-suction.

Dave

Agree that you do not want ProSeal.

Dave shows one way but 25 to 30-years ago while I was building my flying RV-6, I (and others) would sometimes insert a small scrap piece between flange and skin to get a better fit. Yes on one bulkhead, I used the same technique that Dave links to.
 
What are you building? The later pre-punched stuff is really close, even if not perfect. Like David said, metal shims work if the gap is large, but for spots where the skin just gets pulled in *slightly*; just enough to see when the light's right, you can try this trick.

Somebody taught me this trick (used after riveting the structure): Make a 3/4-1" round or square stick, ~4-5" long, out of hardwood. Into one end, about 1/4" from one edge, drill a shallow hole roughly 3/16" dia, big enough to go over a shop head. Taper the end around the hole to ~1/2" diameter, leaving minimal material between hole edge and the closest side.

Have your helper hold a large bucking bar on the outside of the skin, tangent to the curve of the skin at the rivet head. Get in the fuselage with your new tool and a hammer that's about the weight of a regular carpenter's claw hammer or medium ball peen hammer. Place the tool over the rivet in the problem spot, 'narrow' side toward the bulkhead web but tight against the rivet. Bump the tool *very slightly* with the hammer, and have your helper check the skin. This is the realm of science so hard to quantify that it's art.

Repeat the light bumping, increasing force as needed in small increments until you see progress. Stop when you're happy with the result.

What you're actually doing is re-contouring the curve of the bulkhead between web & flange, in the direction that will move the flange outward. As long as the skin wasn't actually creased or stretched, you can usually eliminate the depression.

FWIW,

Charlie
 
Henkil/Hysol make some aerospace liquid shim products, do a search on aerospace liquid shim and you should find some good info.
 
I made a couple dozen shims in various thicknesses and used them as needed all the way from .020 to .125.
 
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